High Peak Power Pulses Research Articles

A compact, high repetition-rate, nanosecond pulse generator based on magnetic pulse compression system

Magnetic pulse compression (MPC) system has been widely-used over a few decades as a technique for producing short duration, high peak power pulses reliably. A compact pulse generator with a 3-stage MPC system (assembled with amorphous cores and ferrite cores) is constructed to generate repetitive pulses of maximum 7.5 MW peak power with pulse width (FWHM) of 70 ns and rise time of 30 ns at the maximum pulse repetition rate of 2 kHz into a 307 resistive load. In this paper, the detailed system design and operational characteristics of the MPC modulator are presented. The MPC has 3-stage pulse compression circuit using two saturable pulse transformers and a magnetic switch. The saturable pulse transformer has two functions, a step-up transformer and a magnetic switch. The generator consists of 2 units with distinct functions. The resonant charge unit is a diode based auto L-C resonator recharger. The 3-stage MPC unit comprises a saturable pulse transformer which compress the pulse width to 1.5 μs and step up the amplitude to 7 kV, and a 2-stage magnetic pulse compressor using another saturable pulse transformer and a magnetic switch, which compress the pulse rise time to 30 ns and step up the amplitude to 62 kV at most (1 kΩ resistive load).

Dynamic parabolic pulse generation using temporal shaping of wavelength to time mapped pulses

Self-phase modulation in fiber amplifiers can significantly degrade the quality of compressed pulses in chirped pulse amplification systems. Parabolic pulses with linear frequency chirp are suitable for suppressing nonlinearities, and to achieve high peak power pulses after compression. In this paper, we present an active time domain technique to generate parabolic pulses for chirped pulse amplification applications. Pulses from a mode-locked laser are temporally stretched and launched into an amplitude modulator, where the drive voltage is designed using the spectral shape of the input pulse and the transfer function of the modulator, resulting in the generation of parabolic pulses. Experimental results of pulse shaping with a pulse train from a mode-locked laser are presented, with a residual error of less than 5%. Moreover, an extinction ratio of 27 dB is achieved, which is ideal for chirped pulse amplification applications.

Ultrafast fiber lasers for strong‐field physics experiments

AbstractThe recent demonstration of rare‐earth‐doped fiber lasers with a continuous‐wave output power approaching the 10‐kW level with diffraction‐limited beam quality proves that fiber lasers constitute a scalable solid‐state laser concept in terms of average power. In order to generate high peak power pulses from a fiber several fundamental limitations have to be overcome. This can be achieved by novel experimental strategies and fiber designs that offer an enormous potential towards ultrafast laser systems combining high average powers (> kW) and high peak power (> GW). In this paper the challenges, achievements and perspectives of ultrashort pulse generation and amplification in fibers are reviewed. This kind of laser system will have a tremendous impact on strong‐field physics experiments, such as the generation of coherent light by high‐harmonic generation. So far, applications in the interesting EUV spectral range suffer from the very low photon count leading to nonrelevant integration times with highly sophisticated detection schemes. High repetition rate high average power fiber lasers can potentially solve this issue. First demonstrations of high repetition‐rate strong‐field physics experiments using novel fiber laser systems will be discussed.

High-energy femtosecond photonic crystal fiber laser

We report the generation of high-energy high-peak power pulses in an all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. The self-starting chirped-pulse fiber oscillator delivers 11 W of average power at 15.5 MHz repetition rate, resulting in 710 nJ of pulse energy. The output pulses are dechirped outside the cavity from 7 ps to nearly transform-limited duration of 300 fs, leading to pulse peak powers as high as 1.9 MW. Numerical simulations reveal that pulse shaping is dominated by the amplitude modulation and spectral filtering provided by a resonant semiconductor saturable absorber.

Polymer-composite fibers for transmitting high peak power pulses at 155 microns

Hollow-core photonic bandgap fibers (PBG) offer the opportunity to suppress highly the optical absorption and nonlinearities of their constituent materials, which makes them viable candidates for transmitting high-peak power pulses. We report the fabrication and characterization of polymer-composite PBG fibers in a novel materials system, polycarbonate and arsenic sulfide glass. Propagation losses for the 60 microm-core fibers are less than 2dB/m, a 52x improvement over previous 1D-PBG fibers at this wavelength. Through preferential coupling the fiber is capable of operating with over 97% the fiber's power output in the fundamental (HE(11)) mode. The fiber transmitted pulses with peak powers of 11.4 MW before failure.

Extremely large-mode-area photonic crystal fibre with low bending loss

We report on the design of a novel flexible very large mode area photonic crystal fibre for short pulse high peak power fibre laser and beam delivery applications. This fibre has an extremely large mode area exceeding 2500 microm(2) when kept straight and over 1000 microm(2) when bent over a 10 cm radius at a wavelength of 1064 nm. In addition our fibre exhibits very small fundamental mode bending loss below 10(-2) dB/m. The large difference between the propagation loss levels of fundamental and higher order modes forces efficient single-mode guidance in the fibre core while bent. This allows using the fibre to build compact high power laser systems. The paper further explores the major features of this fibre including: the dependence of the mode field area on the fibre core shape, the influence of the bending radius and of the bending direction as well as the impact of manufacturing tolerances on the fibre specifications.

Combining microwave beams with high peak power and long pulse duration

The beam combining results with a metal dichroic plate illuminated by the S/X band gigawatt level high power microwaves are presented. According to the previous experiments, the microwave breakdown problem becomes obvious when the peak power and the pulse duration increase, thus, several methods for enhancing the power handling capacity have been considered, and the metal dichroic plates are redesigned to handle the S/X band high power microwaves. Then the design, fabrication, and testing procedure are discussed in detail. The further experimental results reveal that, operated on the self-built accelerator Spark-04, the radiated powers from the S and X band sources have reached 1.8 GW with pulse durations of about 80 ns, and both beams have been successfully operated on the selected dichroic plate without microwave breakdown.

High peak power first, second, and third order Stokes pulses based on intracavity self-stimulated Raman scattering lasers

We obtain high peak power pulses in megawatt range of the first (1181 nm), second (1321 nm), and third order (1500 nm) Stokes radiation from self-conversion of the 1067-nm laser radiation based on Nd:KGW laser. The maximum output energy of the first order Stokes laser is 35.3 mJ, which is to our knowledge, the highest reported energy in an intracavity Q-switched laser. The third order Stokes pulse is obtained in an intracavity Q-switched laser.

Pulse-shaping dynamics controlled by four structural parameters in an all-normal-dispersion mode-locked fiber laser

The characteristics of pulse-shaping dynamics based on four structural parameters in a fiber laser without any dispersion compensation are studied numerically. The simulations show that the four structural parameters, i.e., the location and bandwidth of the spectral filter and the location and output coupling ratio of the output coupler, are crucial for achieving high pulse energy and high pulse peak power in all-normal-dispersion fiber lasers. To obtain high pulse energy and high pulse peak power, optimal positions of the spectral filter and the output coupler inside the cavity are proposed.

Effective cavity dispersion shift induced by nonlinearity in a fiber laser

We report on the experimental observation of high peak power stretched-pulse emission in a dispersion-managed (DM) fiber laser with large positive net cavity dispersion. As stretched pulses are normally observed in DM fiber lasers with around zero cavity dispersion, it suggests that the effective cavity dispersion of a DM fiber laser is not a fixed value but varies with the laser operation conditions. Based on numerical simulations we further show that a stretched pulse could indeed be obtained in our laser under the laser operation condition when a high peak power pulse is formed, suggesting that the effective cavity dispersion shifts with the cavity nonlinearity.

Pulse compression in an electro-optic Q-switched diode-pumped YVO_4/Nd:YVO_4 laser with a Cr^4+:YAG saturable absorber

A diode end-pumped doubly Q-switched YVO4/Nd:YVO4 laser has been realized for the first time to our knowledge by using both an electro-optic (EO) modulator and a Cr4):YAG saturable absorber. A 3.8 ns pulse width is generated by this laser under a pump power of 15 W at 2 kHz, which is obviously compressed in comparison with that of 8.8 ns from a single actively EO Q-switched laser. Under the same conditions, peak power values of 174.7 and 93 kW are also obtained. A coupled equation is given to theoretically analyze the experimental data. The experimental and theoretical results show that the doubly Q-switched laser has the advantages of a shorter pulse width and higher pulse peak power in contrast with a singly Q-switched laser.

Multifilament-core fibers for high energy pulse amplification at 15 μm with excellent beam quality

We report on what we believe to be the first demonstration of an erbium-ytterbium-doped multifilament-core (MFC) fiber for single-mode amplification of narrow linewidth high peak power pulses. A master-oscillator-power-fiber-amplifier laser source has been demonstrated using a 37-filament MFC fiber in the last amplification stage. Pulses with 750 microJ (940 W peak power) and laser linewidth<1 MHz have beam generated with M2 approximately 1.3. This value is close to the theoretical value M2 approximately 1.5.

Analysis of optical pulse coding in spontaneous Brillouin-based distributed temperature sensors

A theoretical and experimental analysis of optical pulse coding techniques applied to distributed optical fiber temperature sensors based on spontaneous Brillouin scattering using the Landau-Placzek ratio (LPR) scheme is presented, quantifying in particular the impact of Simplex coding on stimulated Brillouin and Raman power thresholds. The signal-to-noise ratio (SNR) enhancement and temperature resolution improvement provided by coding are also characterized. Experimental results confirm that, differently from Raman-based sensors, pulse coding affects the stimulated Brillouin threshold, resulting in lower optimal input power levels; these features allow one to achieve high sensing performance avoiding the use of high peak power pulses.

Optimization of pulse width of double passively Q-switched lasers with GaAs and Cr 4+-doped saturable absorbers

Compared with a single passively Q-switched laser, a double passively Q-switched laser with a GaAs saturable absorber and a Cr 4+-doped saturable absorber can produce more symmetric and shorter pulses with high pulse peak power. New normalized coupled rate equations for a double passively Q-switched laser with both a GaAs saturable absorber and a Cr 4+-doped saturable absorber are solved numerically, where the single-photon absorption (SPA) and two-photon absorption (TPA) processes of GaAs are combined. The Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density are considered. The optimization of a double passively Q-switched laser to obtain the shortest pulse width is performed, and a group of general curves are generated for the first time. The curves clearly show the dependence of the optimal normalized parameters on the parameters of the gain medium, the GaAs saturable absorber, the Cr 4+-doped saturable absorber and the spatial distributions of the intracavity photon density. Sample calculations for a diode-pumped Nd 3+:YVO 4 laser with both a GaAs saturable absorber and a Cr 4+:YAG saturable absorber are presented to demonstrate the use of the curves and the related formulas.

Laser-diode pumped self-Q-switched microchip lasers

Optical properties of Cr,Yb:YAG, Cr,Nd:YAG crystals, and composite Yb:YAG/Cr:YAG ceramics self-Q-switched solid-state laser materials are presented. The merits of these self-Q-switched laser materials are given and the potentials of such lasers can be chosen by the applications. Cr,Yb:YAG and composite Yb:YAG/Cr:YAG ceramics self-Q-switched laser are conducted. Although several tens of kW peak power can be obtained with a monolithic microchip Cr,Yb:YAG laser, the experimental results show that the performance of this laser is limited by the absorption of Cr4+ ions at a pump wavelength of 940 nm and strong fluorescence quenching at high Cr concentration. Composite Yb:YAG/Cr:YAG ceramics are more suitable to realize high pulse energy and peak power (up to MW level) with optimized lasing and Q-switching parts. In addition, the instabilities induced by the multi-longitudinal mode competition in Cr,Nd:YAG and Cr,Yb:YAG microchip lasers are addressed. The different gain bandwidths of Yb:YAG and Nd:YAG play an important role in the instability of the output laser pulse trains. Stable laser pulses from the Cr,Yb:YAG microchip laser were obtained due to the antiphase dynamics. For the Cr,Nd:YAG microchip laser, the instability caused by the multi-longitudinal mode competition is an intrinsic property. Different transverse patterns were observed in Cr,Nd:YAG microchip lasers when a pump beam with larger diameter was used. Saturated inversion population distribution inside the gain medium plays an important role in the transverse pattern formation. Different transverse patterns were reconstructed by combining different sets of the Hermite-Gaussian modes.

Q-switched Yb-doped nonlinear microstructured fiber laser for the emission of broadband spectrum

We report on an innovative configuration of a supercontinuum laser based on an Yb-doped nonlinear microstructured fiber. Due to this particular fiber design combining amplification and nonlinear properties, a wideband output spectrum is generated in the fiber under the Q-switched regime. By exploiting stimulated Brillouin scattering, high peak power pulses are achieved and contribute to a spectral broadening due to a nonlinear wavelength conversion process. Both infrared (1000-1200 nm) and visible (650-750 nm) spectra are generated with an average power of 200 mW.

Generation of high-power ultrashort electromagnetic pulses on the basis of effects of superradiance of electron bunches

One of the promising methods for generation of ultrashort electromagnetic pulses (with duration of about ten periods of high-frequency oscillations) is radiation from spatially localized electron ensembles (bunches), which can be considered a classical analog of Dicke superradiance known in quantum electronics. In classical electronics, superradiance can be related to various mechanisms of stimulated radiation. Until now, cyclotron, undulator, and Cerenkov (in the case of interaction with both copropagating and counterpropagating waves) superradiance of electron bunches as well as superradiance during stimulated scattering of a pump wave have been studied theoretically and experimentally. As a result of these studies based on high-current RADAN and SINUS accelerators and their modifications, a new class of oscillators producing pulsed electromagnetic radiation has been created. They have such unique characteristics as pulses of high peak power (up to 1 GW and 3 GW in the millimeter-and centimeter-wave ranges, respectively) and ultrashort duration (from 300 ps to 1 ns, respectively). In this case, regimes with a peak radiation power exceeding the electron-beam power are experimentally realized. Regimes with high (kilohertz) pulse repetition rate and high average power (up to 2.5 kW) are obtained.

Optimization of doubly Q-switched lasers with both an acousto-optic modulator and a GaAs saturable absorber

A doubly Q-switched laser with both an acousto-optic (AO) modulator and a GaAs saturable absorber can obtain a more symmetric and shorter pulse with high pulse peak power, which has been experimentally proved. The key parameters of an optimally coupled doubly Q-switched laser with both an AO modulator and a GaAs saturable absorber are determined, and a group of general curves are generated for what we believe is the first time, when the single-photon absorption (SPA) and two-photon absorption (TPA) processes of GaAs are combined, and the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density as well as the influence of the AO Q-switch are considered. These key parameters include the optimal normalized coupling parameter, the optimal normalized GaAs saturable absorber parameters, and the normalized parameters of the AO Q-switch, which can maximize the output energy. Meanwhile, the corresponding normalized energy, the normalized peak power, and the normalized pulse width are given. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the GaAs saturable absorber, the AO Q-switch, and the resonator. Sample calculations for a diode-pumped Nd3+:YVO4 laser with both an AO modulator and a GaAs saturable absorber are presented to demonstrate the use of the curves and the relevant formulas.

New Experimental Approach to Study Laser Matter Interaction during Drilling in Percussion Regime

Laser drilling is a well-established process in aerospace industry. However quality and geometry of holes do not get under control in an absolute way. Moreover, drilling understanding is complicated due to the number of parameters and physical phenomena. Laser and matter have some own parameters which are not constant with temperature, and so could not be fitted. In this paper, we describe the mechanism of laser-matter interaction for drilling with single and multi-pulse with a new method (called DODO for Direct Observation of Drilled hOle). We show the existence of a threshold between two drilling shapes called conical and round shape. With geometric optic approach, a simple model estimate the drilling depth corresponding to a drilling with round bottom shape. We show the influence of the peak power in a string of pulse on hole morphology (profile, diameter and quality). The influence of peak power fit in the string pulse to eliminate the recast layer cracking. It comes from a solidification of a melt layer on a previous recast layer. To eliminate it from the hole it is essential to melt the previous recast layer with higher peak power pulse than the previous one.

Efficient diode-pumped passively Q-switched laser with Nd:YAG/Cr:YAG composite crystal

Diffusion bonded Nd:YAG/Cr:YAG composite laser crystal has been employed to perform a compact diode-pumped passively Q-switched laser. At the incident pump power of 3.3 W and pulse repetition rate of 16.3 kHz, the maximum average output of 592 mW has been obtained, corresponding to an optical-to-optical conversion efficiency of 18%. Stable passively Q-switched operation with peak power of 6.5 kW and pulse duration of 6 ns was also achieved. It has been experimentally revealed that Nd:host/Cr:YAG composite structure is a promising material for compact cost-effective Q-switched laser sources with high-peak power and short pulse duration. In addition, thermal lens effect (TLE) in the active medium and its impact on the Q-switched laser performance have been analyzed.